Pulmonary Mechanics II

Question 1

pressure-flow relationships

Answer 1

• atm pressure is 0
• 1/3 inspiration, 2/3 expiration
• flow is pressure over resistance
• pressure is Palv-Patm (0 at beginning, so is flow)
• maximum flow at minimum Palv for inspiration (greatest away from 0 negatve) and maximum Palv at mid expiration
• 1 atm= 1030cm h20
• PpL drops initially, Palv drops to -1, flow is negative in
• at break, P is -8
• then goes back to -5
• transmural pressure differences set lung volume

Question 2

transmural pressure

Answer 2

• sets lung volume
• PpL always negative and at minimum at end inspiration so greatest inflation
• curved lines on graph because have to overcome friction and resistance
• PpL more negative than the static values during inspiration and more positive during expiration
• converge at end because resistance only when air is flowing

Question 3

dynamic compliance

Answer 3

• deltaV/deltaP
• obtained from measurements at end inspiration and end expiration
• at start and end of inspiration Palv=Patm, so delta P is -PpL
• typical value is 0.6 L/6 mc h20, 0.1L/cmh20
• should agree with measurements of static compliance is equilibrium is attained at end inspiration and end expiration
• if increased resistance like in disease, dynamic compliance will be less than static-less flow, less air

Question 4

small airway disease

Answer 4

• TV decreases for a given delta P
• dynamic compliance decreases
• misnomer because not actual change in compliance of the lung- just resistance increasing

Question 5

flow

Answer 5

• laminar in trachea, turbulent at each bifurcation
• sounds of quiet respiration
• flow is delta P x piR^4/8n1 in cylinder, laminar
• square root of delta P in turbulent flow
• reynolds number is pvD/n

Question 6

airway resistance

Answer 6

• 20% from tissue
• 80% airway
• frictional only during motion
• use helium instead of nitrogen in resp gas because higher viscosity and lower density, less turbulence, less work
• need more pressure for liquid flow because viscosity is higher

Question 7

airway resistance break down

Answer 7

• small airways 10%
• trachea and bronchi 15%
• glottis 25%
• nose/mouth 50%
• bronchioles not normally main site of resistance but can be in bronchitis

Question 8

resistance continued

Answer 8

• increases for first three divisions (because area actually decreases, velocity increases, air accelerated, resistance increases), then falls as cross sectional area increases
• falls as lung volume increases during inflation
• particles settle in small airway due to decrease in velocity
• delivers air, everything else quickly
• ciliated epithelium of conductive zone cleans system
• smoking causes increase in mucous production, can’t clear anything
• since bronchioles aren’t major site of resistance, disease might be present before you would measure resistance problem

Question 9

epinephrine

Answer 9

• binds with high affinity to B2 receptors
• increases cAMP through Gs
• increase PKA
• phosphorylation of MLCK
• decrease sensitivity of MLCK for Ca/calmodulin
• inhibits binding of myosin cross bridges to actin
• dilates bronchi and bronchioles, reduces resistance
• enhances breathing

Question 10

factors affecting airway resistance

Answer 10

• neural innervation is sparse
• SNS dilation of bronchial smooth muscle by epi
• PNS constriction through vagus nerve on muscarinic receptors
• reflex constriction-smoke particles, noxious gases, extreme cold
• histamine is bronchoconstrictor but vasodilator-H1 receptor
• inflammatory swelling of bronchiol mucosa
• PEEP- positive end expiratory pressure decreases resistance

Question 11

isovolume pressure-flow curves

Answer 11

• *resistance to expiration increases at low lung volumes
• constructed from simultaneous measurements of flow rates, lung volumes, and alveolar pressures during a series of forced expirations each more rapid and vigorous until a maximal effort is made
• replotted to show dependence of flow on pressure at constant lung volume
• at low lung volumes, increasing pressure leads to a maximal flow rate
• maximal flow rate increases with increasing lung volumes
• when flow is maximal, V=P/R=k, constant, so R is increasing in direct proportion to P
• increase in resistance with increasing Palv is due to dynamic compression
• no plateau during inspiration

Question 12

dynamic compression

Answer 12

• partially collapses airways and equal pressure point moves closer to alveoli with greater expiratory efforts
• Palv is 5 and decreases
• PpL positive for forced expiration, Palv now 20

Question 13

equal pressure point

Answer 13

• point where P airway equals PpL
• toward the mouth. airway P < PpL and dynamic compression can occur
• more pronounced at lower lung volumes because lung is more compliant
• increased compliance, more airway will close during expiration, difficulty exhaling
• pushing harder with the chest increases PpL and EPP moves closer to alveoli, compressing airway and increases resistance